Problem with brake swap.

^^^All of that^^^, plus how long has the car sat, is there actually
any pressure at the port of the MC if you bleed it? Sounds like you
need to pick up the correct MC anyway,and most any OE mopar
metering valve unit from a car will work from the '73& up to the newer(RWD) aluminum MC's . They're not rare yet,get one,be happy.
Assuming 11" drums on an A-body 8.75,why? Just sayin', it's
on the drum for you to read,and it wouldn't come that way OE. If
they are 11', you may be able to step down to a smaller dia. set of
wheel cyls. to help balance the brake bias.